This invention relates generally to forming a barrier layer on the surface of an enclosed vessel in order to render it impermeable to hydrocarbon liquids and gases, and more particularly to an apparatus and method for sulfonating an article and the articles made thereby.
As everyone knows, air pollution is a problem for our society, and controls have been placed on the acceptable levels of various emissions allowable by law. Automobiles and their various components are especially susceptible to controls for gaseous emissions into the air. Air pollution is not only measured by the amount of emissions coming out of the tailpipe of a vehicle during operation, but also the amount of pollution it creates just sitting there. After the vehicle is turned off, hydrocarbon fumes permeate through the plastic gas tank and escape into the atmosphere, thereby creating more air pollution, even though it is not pollution which comes from the tailpipe. It has been found that measurable amounts of gasoline permeate through the plastic gas tanks and evaporate into the air, causing further air pollution. In addition to gasoline tanks, the complementary caps, filler necks, and rollover valves are generally made from blow molded plastic compounds, also found to readily be permeated by oleophilic materials, including gasoline and other liquid hydrocarbons. Similar concerns arise for bottles and containers for hydrocarbon solvents, or any other liquid hydrocarbon container or component. In the recent past, various attempts have been made to prevent that permeation, including the use of barrier layers, multi-layer configurations and surface treatments.
One such prior art attempt included the use of a sulfur-containing gas to contact the inner surface of a gasoline tank, thereby creating a sulfonation barrier layer to prevent permeation of gasoline. Generally speaking, these gasoline tanks are made of a sulfonatable polymer, i.e. one which has hydrogen atoms bonded to the carbon atoms replaceable by sulfonic acid groups. For example, polypropylene, polyethylene, polybutylene, and other plastics are sulfonatable, while polytetrafluoroethylene would not be sulfonatable.
These surface sulfonatable polymers have previously been sulfonated with sulfur trioxide gas. This conventional method is relatively slow and very expensive, and gave an undesirable rinseable salt on the inside of the tank. The prior art methods for sulfonating included placing the entire gasoline vessel and/or its complementary components into a chamber, evacuating the chamber of air and re-introducing sulfur trioxide gas. Needless to say, this method is slow and uses a great deal of sulfur trioxide gas, which in itself is a significant problem for the environment.
Other methods for creating a barrier layer on gasoline tanks, as well as other vessels for containing hydrocarbon liquid materials, such as various solvents, including toluene, benzene and the like, have included the use of blow molding multiple layers of plastic, including various components which act as barrier layers. Until recently, the standard for barrier layers included a multi-layer plastic embodiment which was practiced by suppliers to the automotive industry. The multiple layers were formed during the blow molding stages and these procedures are relatively fast and easy to manufacture utilizing conventional methods. However, the permeability to gasoline is not acceptable for new EPA standards, and the sulfonating technique has been revisited, even though it previously had problems with speed and ease of application.
Therefore, it is an object of the present invention to provide an apparatus for rapidly, inexpensively and efficiently sulfonating the surface of an article with a sulfonating gas to modify and treat the surface in order to provide a hydrocarbon impermeable material to be used as a storage means for such liquids and/or gases. It would be especially advantageous to utilize an inexpensive source of sulfur, and recycle and reuse the sulfur trioxide gas such that essentially none of it is released into the atmosphere.
It is yet another object of the present invention to provide such an apparatus which can quickly and inexpensively apply the sulfonating technique to the surface of a storage vessel.
It is yet another object of the present invention to provide an apparatus for sulfonating the surface of polymeric articles, including a multi-port gas delivery system with individual ports for xe2x80x9cfillingxe2x80x9d a multitude of vessels for sulfonating simultaneously.
It is still yet another object of the present invention to provide a method for sulfonating an article to effect a surface treatment which quickly and inexpensively provides a sulfur-containing gas to effect the sulfonation, as well as the articles made therefrom.
It is yet a further object of the present invention to provide a method for sulfonating a hydrocarbon-containing vessel which will comply with the EPA and the various regulations for many states regarding the storage and transport of toxic and hazardous materials in these vessels.
In accordance with the preferred embodiments of the invention, these and other objects of the invention are addressed as follows. An apparatus for sulfonating the surface of an article with a sulfonating gas to modify and treat the article is disclosed which includes an enclosable container which is substantially airtight to contain substantially all of the sulfonating gas, a gas inlet for introducing the gas into the container, and an on-site and on-demand sulfur-containing gas generator utilizing a chemical feed stock selected from the group consisting of raw sulfur, processed sulfur, sulfur dioxide, liquid sulfur dioxide, sulfur trioxide, sulfuric acid and mixtures thereof, to produce the sulfur-containing gas on site at a predetermined concentration. The disclosed apparatus also includes a source of dry air for mixing with the sulfur-containing gas and a pump for pumping the gas into the enclosable container. The apparatus may further include an in-line heater to heat the dry air, as well as a sensor for monitoring the concentration of sulfur in the sulfur-containing gas after it has been exhausted from the container after the sulfonation process has been complete. By monitoring the sulfur concentration with the sensor, the monitor may be adapted to trigger the on-site gas generator to make more sulfur-containing gas, thereby maintaining the optimum concentration of sulfur in the gas which is introduced into the next batch in the enclosable container holding the articles to be sulfonated.
In another embodiment of the present invention, another apparatus is disclosed for sulfonating an enclosed vessel, such as an automobile gasoline tank, with sulfonating gas to modify and effect a treatment on the interior surface of the vessel. This apparatus includes at least one inlet to be inserted into the opening of the enclosed vessel for injecting sulfonating gas into the vessel in a substantially airtight seal. Preferably, this apparatus may include a multi-port delivery system so that a multitude of enclosed vessels, such as a gasoline tank, can be sulfonated at one time. Again, there is present the on-site and on-demand sulfur-containing sulfonating gas generator as described above, with a source of dry air for mixing with the sulfur-containing gas. A pump included in the apparatus pumps the sulfonating gas through the injection inlets, whereby the interior surface of the gasoline tank or other enclosed vessel is sulfonated. An optional sulfur concentration sensor or monitor can be used to maintain the sulfur levels in each new application.
These two above embodiments disclose the apparatuses usable for both automotive gasoline tanks and for the smaller components that are required for assembly within an automobile, including, but not limited to, gas caps, filler necks, rollover valves and the like. Needless to say, the enclosable vessels can be sulfonated by injecting gas into the vessel, while the other accessories can be sulfonated by placing them into an enclosed container and subjecting them to a sulfonation gas. Both systems are substantially airtight, so that when a sulfonating gas is injected either into the enclosed container or directly into the enclosed vessel itself, the exhaust gas can be monitored for its sulfur concentration, and a sulfur concentration makeup system can be activated with the on-site and on-demand sulfonating gas generator. These apparatuses essentially utilize all of the sulfur-containing gas without release into the atmosphere, as the release of sulfonating gas would be an environmental tragedy.
In order to automate this operation, another embodiment of the present invention is disclosed which includes an apparatus for applying a treatment or surface modification onto the surface of polymeric articles including the multi-port gas delivery system described above, with means for containing and transporting the sulfonating gas and recycling and delivering to a continuous supply of polymeric articles to be sulfonated. Further, this apparatus, along with the ones described above, may also include a means for introducing a neutralizing agent to neutralize the surface of the sulfonated polymeric articles after they have been sulfonated.
In another embodiment of the present invention, yet another object of the present invention is accomplished with the following methods. Disclosed is at least one method for sulfonating an article to effect a surface treatment, including the steps of placing at least one article in an enclosable container, the container being capable of being substantially airtight. Sulfonating gas is generated on-site and pumped into either the enclosable container with parts or articles therein, or directly into the interior of an enclosable vessel, such as a gas tank. After the sulfonation treatment is accomplished, the gas is exhausted, ready to be rejuvenated and recycled, and the sulfonated surface may be neutralized by contacting with a neutralizing agent, such as a positive ion-containing fluid. After the neutralizing agent is removed, the article is ready to be put into service.
Therefore, new apparatuses and methods for sulfonating an article and articles made therefrom are disclosed which meet the objects and advantages of the present invention.